Higher plants are sessile organisms. They are rooted to the soil and are unable to move away from harsh environmental conditions. They stand cold winters, hot and dry summers, floods that submerge them, and the salinity of the soil as well as drought that dehydrates them. But, plants have been doing this for millions of years and can adapt to such conditions by making use of an array of mechanisms evolved to fight the stress. They even evolved to either restrict their life-cycle to months that are amenable for growth, or they complete the reproductive phase during those months and enter a phase of restricted metabolism in order to tide over the stressful period. Due to increasing world population and pollution, environmental conditions are changing fast. Increasing need for food and consumer preferences necessitate crop plants to be grown in regions where they are not naturally adapted, leading to various stresses.
Stress in all it forms has negative effects on plant development and productivity. Plants respond to salinity by reduced leaf growth and inhibition of cell division and expansion. The decrease in the osmotic potential of root cells leads to inhibition of water uptake and dehydration of the plants. Subsequently, excessive accumulation of salt leads to death of tissue, organ and eventually whole plant Chilling-stress stunts plant growth, brings about cellular autolysis and senescence, as well as has detrimental effect on flower induction, pollen production and germination. Chilling and desiccation stresses damage cell membranes. Oxidative-stress targets membranes, proteins and DNA.
The development and survival of plants is constantly challenged by changes in environmental conditions, namely fluctuations in temperature, paucity of water, salinity, flooding, metal toxicity and mechanical injury. In order to tide over these adversities, plants elicit complex physiological and molecular responses. Stress is perceived and transduced through a chain of signaling molecules that ultimately affect regulatory elements of stress-inducible genes to initiate the synthesis of different classes of proteins including transcription factors, enzymes, molecular chaperons, ion channels and transporters or alter their activities. Such cascading events controlled by a battery of genes and their intricate regulation help the system to tide over the unfavorable conditions. According to some estimates, plants possess somewhere between 25,000 to 55,000 genes (Kamalay and Goldberg, 1980, 1984; The Arabidopsis Genome Initiative, 2001; Burr, 2002; Goff et al., 2002; Yu et al., 2002). Many of these are ‘housekeeping’ genes that express in all the tissues, while others are organ-specific or regulated by environmental cues. In order to understand the process of development of plants and their response to environmental stresses, it is imperative to know the function of crucial genes and their regulation during different phases of the life cycle (Ausubel, 2002; Ronald & Leung, 2002). Conventional mutation genetics and cloning of the corresponding genes as well as new approaches, like differential screening, subtractive hybridization, differential display, microarray analysis, along with reverse genetics, have been used to clone such genes and define their function (Brent, 2000; Tyagi and Mohanty, 2000; Aharoni and Vorst, 2001).
Rice is the most important food crop as well as a model monocot system (Khush, 1997; Tyagi et al., 1999; Cantrell and Reeves, 2002). However, the production of rice should increase by 60% in next 25 years in order to keep pace with the growing world population. Minimization of the loss due to biotic and abiotic environmental factors can not only help improve net production but extend rice cultivation in marginal and non-cultivable lands (Khush, 1999; Tyagi and Mohanty, 2000). Therefore, the production of a plant, exhibiting tolerance/resistance to various abiotic stress is required. Functional genomics in rice is thus an important area of research whereby function of new genes involved in plant development and survival is defined. Discovery of genes involved in environmental stress responses provides new targets for genetic engineering of rice and other crops for better tolerance/resistance. Therefore, there is a need in isolating and characterizing novel genes of rice and characterizing these novel genes for their various functions. Different screening strategies were employed to isolate genes from elite indica rice (Oryza sativa L. var. Pusa Basmati 1) that are expressed in an organ-specific manner or are induced by stress. In this invention, we describe the identification, isolation, characterization and use of a novel gene, OSISAP1, encoding a zinc-finger protein that is differentially expressed in various organs and induced by several stresses. This invention also relates to a method of over-expressing the novel gene OSISAP1 encoding a zinc-finger stress associated protein from rice conferring salt, cold and drought stress tolerance in transgenic plant systems. This invention also relates to transgenic plants, plant tissues and plant seeds having a genome containing the novel gene OSISAP1 and a method of producing such plants and plant seeds.